Polymerization of ethylene with (nBuCp)2ZrCl2 supported over mesoporous SBA-15 functionalized with sulfonic acid groups
The polymerization of ethylene in n-heptane with (nBuCp)2ZrCl2 supported over mesoporous SBA-15 catalysts functionalized with propyl or aryl sulfonic acid groups and impregnated with either MAO or TMA was investigated and compared with reference samples. All the supports showed mesoscopic ordering with pore sizes of 7.8–6.6 nm, BET surface areas around 700 m2 g−1, sulfonic acid loadings between 10 and 20 wt% and an acidity of roughly 1–1.7 mmol H+ g−1. None of the catalysts were capable of polymerizing ethylene in the absence of MAO in spite of using TMA or TIBA as scavengers. The addition of MAO (Al/Zr = 800 or 5000) led towards ethylene polymerization, being the activity dependent on Al/Zr molar ratio (higher for Al/Zr = 5000). The catalysts treated with TMA during the impregnation exhibited considerable leaching, unlike those treated with MAO wherein the leaching was low (<9 wt%). The presence of the sulfonic acid moiety enhanced the activity of the catalysts. In addition, the activity was also augmented with the increase of the sulfonic acid content from 10 to 20 wt%. Interestingly, the molecular weight of the polyethylene synthesized with the SBA-15 functionalized with sulfonic acid groups were 1.5–2.5 times higher, especially with the propyl moiety which leads towards Mw ∼ 350,000 g mol−1 at 1.2 barg. The results were explained through an interaction between the sulfonic acid moiety and the chlorinated MAO species, which activates the metallocene.
Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (74 K)Download as PowerPoint slideHighlights► MAO was required to activate the metallocene, despite the sulfonic groups. ► Catalysts impregnated with TMA displayed considerable leaching of the metallocene. ► The activity increased with the content of sulfonic acid group and the acid strength. ► The sulfonic group and the chlorinated MAO might interact activating the metallocene.
Journal: Applied Catalysis A: General - Volumes 437–438, 26 September 2012, Pages 44–52